1. Field of the Invention
The present invention relates to a control system for an air conditioning unit for controlling the humidity and temperature of interior building space at desired levels regardless of the outside temperature and humidity conditions. More specifically, the present control system employs a combination of return air bypass, variable capacity compressor, and modulating hot gas reheat to maintain proper interior space humidity, and temperature while maintaining adequate ventilation within the interior building space. By combining these three control mechanisms, the system is also able to operate more efficiently and with less energy consumption.
2. Description of the Related Art
The present invention relates to a control system for an air conditioning unit for controlling the humidity and temperature of interior building space at desired levels regardless of the outside temperature and humidity conditions. Presently, there are no HVAC systems, with the exception of very large and expensive units that employ chilled and heated water, that are able to maintain both a desired temperature and a desired humidity in an interior building space. These existing units are used only in very limited applications because of the complexity of the systems and the cost.
With the increasing public awareness of the health problems associated with the occurrence of mold in interior building space, the need to control humidity in these spaces is becoming more urgent, particularly in public buildings such as schools. Typically, mold will grow inside a building when the humidity level is at or above 50% saturated. Mold grows particularly well when the humidity is above 50%. The ideal humidity for the interior of a building in order to prevent the growth of mold is approximately 45%. Current HVAC systems are unable to maintain humidity levels inside a building below 50% saturated under all outside temperature and humidity conditions. Some current HVAC systems employ reheat to try to achieve desired interior humidity levels, but the energy efficiency of the unit goes down when reheat is employed.
The present system is able to constantly maintain desired temperature and humidity levels inside a building space while maintaining adequate ventilation within the interior building space under any outside air conditions. The present invention does this by simultaneously employing a combination of modulated return air bypass, variable or modulated capacity compressor, and modulated hot gas reheat to simultaneously control the humidity and temperature. Also, the present invention operates in an efficient manner so that the present invention consumes less energy and operates at less expense than HVAC units that are not able to achieve this high degree of temperature and humidity control.
The present system provides linearly control in that the temperature and humidity of the interior building space remains constant. The system provides smooth, steady operational control, rather than having the humidity and temperature fluctuating up and down.
Also, the present system provides tight humidity control, maintaining the desired 45% humidity at all times within the interior building space.
In essence, the present invention is a dynamic control system that works so much better than current HVAC systems that it is able to accomplish what other HVAC systems can not do in the way of simultaneously controlling interior space temperature and humidity while maintaining adequate ventilation, and it does it at less cost than current units.
The present invention is a control system for a HVAC system that is capable of constantly maintaining desired temperature and humidity levels inside a building space while maintaining adequate ventilation within the interior building space under any outside air conditions. The present invention does this by simultaneously employing a combination of modulated return air bypass, variable or modulated capacity compressor, and modulated hot gas reheat to simultaneously control the humidity and temperature. These three controls are monitored and their operation is controlled by a controller that modulates their operation and the operation of the unit.
The controller monitors the temperature and humidity of the air of the interior building space. The controller modulates the compressor to control the temperature of the interior building space at the desired temperature set point, i.e. usually about 75 degree Fahrenheit. In order to control the humidity of the interior building space at the desired humidity set point, i.e. usually about 45% saturated, the controller first modulates the return air bypass damper as far as possible without allowing the evaporator coil from getting too cold as indicated by monitoring the suction pressure at the coolant exit of the evaporator and preventing the suction pressure from going below a low pressure limit. If this does not produce a humidity that satisfies the humidity set point, after the return air bypass damper is fully modulated, the controller next modulates the hot gas reheat to achieve the desired humidity control.
When reheat is employed, the system utilizes a temperature sensor in the supply air line to provide feed forward control to the compressor by sensing change in the temperature of the supply air before the temperature of the interior building space goes out of control. When the supply air temperature sensor sees an increase in temperature, the controller modulates up the compressor to increase the compressor""s capacity to pump more coolant to the evaporator. Thus, both the feed forward control and the temperature sensor in the interior building space can serve as the basis on which the controller modulates the compressor to control the temperature of the interior building space.
Also, in order to save even more energy, once the system has satisfied the humidity set point for the interior building space, the system will reset the low pressure limit for suction pressure at the coolant exit of the evaporator, thereby minimizing the use of reheat. This allows the system to operate most efficiently by producing the highest leaving air temperature out of the evaporator while not going too high so that it does not properly dehumidify the air.
Also, the control monitors the pressure drop across the outside air damper and controls the return air damper and the outside air damper to insure that adequate outside air enters the HVAC system to maintain adequate ventilation in the interior building space. Alternately, instead of employing pressure drop across the outside air damper, the system can employ a carbon monoxide sensor located in the interior building space to regulate the amount of outside air entering the HVAC system in order to meet the oxygen demands of the occupants of the building.
The present invention operates in an efficient manner so that the present invention consumes less energy and operates at less expense than HVAC units that are not able to achieve this high degree of temperature and humidity control. In essence, the present invention works so much better than current HVAC systems that it is able to accomplish what other HVAC systems can not do in the way of simultaneously controlling interior space temperature and humidity, and it does it at less cost.